PROJECT SUMMARY Asthma fatalities are rare and often sporadic. However, they are not inevitably the result of poor compliance with treatment programs and in some cases can afflict even mild asthmatics. While typical asthma is characterized by reversible airway obstruction and robust eosinophilia, sudden-onset fatal asthma presents with prominent airway neutrophilia and death within a few hours of initiation of the attack. It remains an enigma that is clinically very challenging to treat. Preliminary data show exposure to Pseudomonas aeruginosa and Aspergillus fumigatus in the allergen-sensitized lung results in massive bacteremia, robust neutrophilic inflammation, pulmonary edema, and lung hemorrhage. Based upon these data, we have formulated a central hypothesis that allergy provides a pulmonary environment where bacterial growth is aided by fungal nutrient scavenging of iron, allowing bacterial overgrowth and an ineffective granulocytic response that contributes to the pathologic state. The proposed studies are intended to provide practical information for the modification of current experimental and clinical protocols in order to identify risks and guide improved treatment options. To test our hypothesis, we propose these specific aims: Specific Aim 1. To determine the extent to which the interaction of fungal and bacterial microbial products promotes bacterial overgrowth in the allergic lung. Using in vivo and in vitro assays, we will test our working hypothesis that fungal siderophores are used by bacterial microbes to enhance growth, causing a cascade of fatal pulmonary pathology. Specific Aim 2. To determine the extent to which allergic status exacerbates pulmonary pathology after fungal-bacterial co-exposure. Using in vivo modeling, as well as cellular and molecular techniques, we will test our working hypothesis that the allergic lung provides insufficient stimulation to fully engage recruited neutrophils resulting in pulmonary collapse. We propose an innovative approach to examine the initiation and progression of fatal and near-fatal asthma. This is a critical step in understanding the chain of events of fungal allergic asthma so that evidence- based management practices can be developed for clinical applications, alleviating the physical and financial burden of this disease and limiting risk of sudden death. In addition, microbial siderophores are a potential therapeutic target that could prove useful in chronic colonization by either or both of these common pulmonary pathogens.!